1. Field of the Invention
The present invention relates to a levelling machine, particularly for levelling sheet steel and strip steel. The levelling machine includes upper and lower leveller rolls which are arranged offset relative to each other. The leveller rolls are supported over the length thereof by means of back-up rolls arranged in roll stands and supported, in turn, by transverse crossbeams. At least the upper transverse cross beam is adjustable for positioning the leveller rolls by means of adjusting cylinders. Compensating cylinders are arranged between the roll stand and the transverse crossbeam.
2. Description of the Related Art
Levelling machines are known in the art in which the back-up rolls can be pre-adjusted in such a way that, taking into consideration the bending of the transverse crossbeams as a result of the levelling force, the bending of the levelling rolls is compensated and, thus, the leveller rolls are straight during levelling. For this purpose, the levelling machines may have upper and lower transverse yokes or crossheads and changing cassettes which are divided in the middle vertical transverse plane of the leveller rolls and are connected by joint connections in such a way that the cassette components including the groups of back-up rolls for the leveller rolls supported by the cassette components can easily be adjusted into a V-shape under idle running conditions. As a result of the levelling force, the crossheads are bent to such an extent that the preadjusted V-shape is cancelled, the groups of back-up rolls are in axial alignment and, thus, the leveller rolls are straight which is equivalent to a compensation of the bending of the crossheads. The crossheads, or at least the upper crosshead, are obliquely adjustable as a unit in the travel direction of the material being levelled by means of two pairs of adjusting devices which are supported on the machine columns, so that the depth of immersion of the offset leveller rolls can be adjusted so as to decrease from the entry side of the material to be levelled to the exit side for the distribution of overstretching. A different depth of immersion of the lower and upper levelling rolls which are arranged offset to each other serves for the adaptation to the column elongations which change or differ during entry and exit of the levelled material from the levelling machine.
In addition, the leveller rolls must be in contact even under idle running conditions with the groups of back-up rolls which are also arranged in a V-shape, which means that the leveller rolls must be pre-bent into a V-shape by means of forces acting on the ends thereof. Because of the substantially tilted position of the groups of back-up rolls, the extent of the prebending of the leveller rolls must be significant, so that the leveller rolls are subjected to significant bending forces until they are bent into the straight shape under the levelling force. Finally, there is the problem that in spite of the tilting yoke adjustment, the upper roll stand must be centered with the lower roll stand, so that an exact parallel position of the work rolls can be achieved and an always uniform gap or uniform pass line is possible. In addition, it is desirable to avoid complicated ball-and-socket joints and heavy ball-and-socket joint piles for transmitting the levelling forces.